1. Field of the Invention
The present invention relates to an apparatus for treating a medical liquid which includes a treatment machine having coupling surface, with a cassette made of a hart part having liquid-conducting passages which are covered by a flexible film being able to be coupled to the coupling surface of the treatment machine. The present invention further relates to a medical cassette made of a hard part having liquid-conducting passages which are covered by a flexible film, with the cassette being able to be coupled to the coupling surface of the treatment machine. The present invention further relates to an apparatus for treating a medical liquid which includes a treatment machine having a coupling surface, with a cassette made of a hard part having liquid-conducting passages which are covered by a flexible film. The present invention further relates to a method for coupling a cassette made of a hard part having liquid-conducting passages which are covered by a flexible film to the coupling surface of a treatment machine for the treatment of a medical liquid as well as to a method for checking the leaktightness of such a medical cassette.
2. Description of the Related Art
The treatment machine can be a blood treatment machine such as is used in hemodialysis or in peritoneal dialysis. In such a use, the medical cassette includes the blood-conducting or dialysis liquid-conducting passages and is in communication with actuators and sensors of the treatment machine via the coupling surface. The medical cassette can thus be configured as a cost-effective disposable part, whereas the actuators for the control of the liquid flow through the cassette and the sensors are integrated into the treatment machine for the level detection or for the pressure measurement.
Such medical cassettes configured as disposable articles comprise in this connection a thin-walled three-dimensional hard plastic part having a planar peripheral contact edge and various recesses (chambers, webs and passages). Medical liquids such as dialysate or blood can now be conducted in the chambers and passages formed by these three-dimensional structures of the hard plastic part. The contact plane of the cassette is closed in a liquid tight manner by a flexible film, advantageously a polymer film which is peripherally connected, in particular welded and/or adhesively bonded, to the contact edge of the hard part. The medical cassette is pressed onto the coupling surface of the treatment, machine in use with the flexible film so that actuators and sensors of the treatment machine lie on the polymer film. In addition, the flexible film is pressed together with the webs of the cassette by this pressing and thus provides a fluid tight separation of the liquid-conducting passages in the hard part by the webs and the flexible film.
The coupling surface of the treatment machine accordingly usually has actuators, sensors and pressing force transmission surfaces. The actuators and sensors of the blood treatment machine are arranged in this context in the coupled state of the cassette opposite the liquid-conducting passages of the cassette. The actuators can hereby form valves by the pressing down of the film in that the flexible film is pressed into regions of the liquid-conducting passages and closes them. The sensors, for example, measure the pressure or temperature of the liquid located in the liquid-conducting passages. The pressing force transmission surfaces press the flexible film against sealing webs of the hard parts which surround the liquid-conducting passages to seal them with respect to one another and toward the rest of the cassette. In this connection, the coupling surface is usually formed by a planar surface of a support member which is made from metal, for example, with receivers for the sensors and the actuators being provided in the surface, and by the sensors inserted into these receivers in planar fashion.
A flexible mat made, for example, of silicone or another elastomeric material, is usually arranged on the coupling surface of the treatment machine. This has the advantage that the sensor surfaces are protected against environmental influences and the machine surface is moreover liquid tight and thus may ideally be hygienically cleaned. The flexible mat in this context represents a part of the treatment machine to which the cassette is coupled as a disposable part. The operation of the actuators is ensured by the flexibility of the mat. In addition, the flexible film can be pressed well to the coupling surface via the flexible mat, which permits a good contact with the actuators, sensors and pressing force transmission surfaces. The treatment machine can, however, also be operated without a flexible mat so that the flexible film lies directly on the coupling surface and the sensors and actuators couple directly to the film.
There is, however, the difficulty with known systems in the coupling of sensors to the film surface of achieving a good coupling to obtain correct measured values. In particular, air which is trapped in the transmission path between the flexible film and the sensor surface on the insertion of the cassette, produces a falsification of the measured results. This applies to pressure sensors (in particular on the measurement of pressures which are less than the environmental pressure), but also in level detection and likewise to actuators such as valves. Unwanted air inclusions between the outer surface of the flexible film and the mat surface of the flexible mat lying thereon or, if no mat is used, of the coupling surface of the treatment machine lying thereon, should therefore be eliminated on the coupling. This usually takes place by air suction. In this context, however, the fluid contacting of this space is complicated. There is in particular the problem that a self-sealing of the film takes place by an application of the film onto the mat or onto the coupling surface so that air islands remain.
It is therefore known from DE 101 57 924 C1 and DE 102 24 750 A1 to realize the air transport by means of integrated mat passages, predetermined in a defined manner, on the rear side of the machine mat at the machine side. The air line from the surface of the flexible film through the mat to the air passages arranged on the machine side takes place locally through uninterrupted slots in the region of the mat passages. The air transport however, hereby only takes place at precisely defined points of the flexible film of the cassette at which the air is sucked off through the slots in the mat to the mat passages arranged on the machine side. These mat passages therefore have to be located in the region of the liquid-conducting passages of the cassette to ensure a good suction there, which can lead to safety problems. Such a machine mat having integrated mat passages and slots is moreover cost-intensive in manufacture and complex and/or costly in cleaning. The sensor surface is thus also no longer ideally protected from environmental influences and hermetically sealed by the mat so that hygienic problems also result. There is moreover the need to further improve the reliability of the air suction since the inclusion of air islands can still occur due to the only local suction through the slots.